Variable valve-operating system for internal combustion engine

ABSTRACT

A variable valve-operating system for an internal combustion engine, comprising a cylinder head having an intake or exhaust valve, a camshaft rotatably supported by the cylinder head, a cam body rotatably fitted around the camshaft and including a cam lobe having an outer peripheral surface for driving the valve and a boss protruding radially from the cam body, and a valve open period-varying mechanism supported on the camshaft and including an intermediate rotating member having a center of rotation offset from the camshaft, the mechanism transmits rotation of the camshaft to the boss of the cam body through the intermediate rotating member and also permits the valve open period of the valve to be varied through adjustment of the eccentric phase angle of the intermediate rotating member, wherein at least a part of the boss is so positioned as to overlap with the profile of a nose of the cam lobe when viewed in the axial direction of the cam body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable valve-operating system for varying the valve open period of valves of an internal combustion engine.

2. Description of the Related Art

Variable valve-operating systems for varying the valve open period of intake or exhaust valves in accordance with operating conditions of a reciprocating engine (internal combustion engine) mounted on a motor vehicle have been developed in order to suitably control the characteristics of the intake or exhaust valves.

For example, Unexamined Japanese Patent Publication No. H10-280925 discloses a variable valve-operating system comprising a cam lobe rotatably fitted around the outer peripheral surface of a camshaft supported by a cylinder head, and a valve open period-varying mechanism for transmitting rotation of the camshaft to the cam lobe while periodically varying the rotation speed. Specifically, the valve open period-varying mechanism includes a harmonic ring (intermediate rotating member) fitted around the outer peripheral surface of the camshaft adjacently to the cam lobe and eccentrically rotatable around the camshaft. The harmonic ring converts constant-angular-velocity rotation of the camshaft driven by the crankshaft of the engine to non-constant-angular-velocity rotation whose rotation speed periodically varies, and the cam lobe to which the non-constant-speed rotation is transmitted drives the valve with its nose. The eccentric axis of the harmonic ring is adjusted to change the retard or advance angle of the cam lobe relative to the rotational angle of the camshaft, thereby varying the valve open period.

The valve open period-varying mechanism disclosed in the above patent publication includes a boss protruding radially outward from an end portion of the body of the cam lobe, in order to transmit the non-constant-speed rotation of the harmonic ring to the cam lobe. The non-constant-speed rotation of the harmonic ring is input to the boss. Specifically, a connector pin is rotatably supported at one end by the boss of the cam body and is slidably engaged at the other end with a slide groove cut in the opposing end face of the harmonic ring so that the non-constant-speed rotation of the harmonic ring may be transmitted to the cam lobe.

The boss of the cam body is located at a desired phase angle with respect to the nose of the cam lobe. In most cases, the boss is located diametrically opposite the cam nose, as disclosed in the aforementioned patent publication.

In order for the boss to be coupled with the harmonic ring by the connector pin, the boss should have a size large enough to project outward from the base circle of the cam lobe. Moreover, since the boss is located adjacent to the cam lobe, restrictions are imposed on the boss such that the projecting part of the boss should not interfere with the valve lifter. For this structural reason, stress is liable to concentrate at the base of the boss where the boss is connected to the cam lobe.

To overcome the drawback, the base of the boss and its peripheral part may be increased in thickness to secure rigidity and mechanical strength high enough to withstand the stress concentration.

It is, however, considerably difficult to increase the thickness of the base of the boss and its peripheral part, because the boss must not interfere with the valve lifter (follower) disposed in sliding contact with the cam lobe. Further, since the boss has to be located near the valve lifter, it is not possible to provide the boss with a reinforcing member.

In some engines equipped with a variable valve-operating system, therefore, the maximum rotation speed of the engine has to be lowered in order to lessen the load applied to the boss, making it impossible to take full advantage of the performance that the engine can offer.

SUMMARY OF THE INVENTION

The present invention was made to solve the above problems, and an object thereof is to provide a variable valve-operating system for an internal combustion engine which permits the base of a boss of a cam body to be increased in rigidity.

To achieve the object, the present invention provides a variable valve-operating system for an internal combustion engine. The variable valve-operating system comprises: a cylinder head having an intake or exhaust valve; a camshaft rotatably supported by the cylinder head; a cam body rotatably fitted around an outer peripheral surface of the camshaft, the cam body including a cam lobe having an outer peripheral surface for driving the valve, and a boss protruding radially outward from an end portion of the cam body; and a valve open period-varying mechanism supported on the camshaft and including an intermediate rotating member having a center of rotation offset from an axis of the camshaft, the valve open period-varying mechanism being adapted to transmit rotation of the camshaft to the boss of the cam body through the intermediate rotating member and also permitting a valve open period of the valve to be varied through adjustment of an eccentric phase angle of the intermediate rotating member, wherein at least a part of the boss is so positioned as to overlap with a profile of a nose of the cam lobe when viewed in an axial direction of the cam body.

According to the present invention, the part of the cam body between the boss and the cam lobe can be increased in thickness up to the profile of the cam lobe, whereby the rigidity of the base of the boss can be markedly enhanced by the increased thickness.

Preferably, the boss is so positioned as to be located inside of the profile of the nose of the cam lobe when viewed in the axial direction of the cam body.

In the preferred variable valve-operating system, the boss of the cam body does not interfere with a follower of the valve at all, because the boss moves together with the nose of the cam lobe while being located inside of the profile of the nose as the valve is pushed down by the cam lobe and then returned. The part of the cam body between the boss and the cam lobe can therefore be increased in thickness, thus increasing the rigidity of the base of the boss.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirits and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:

FIG. 1 is a sectional view of a variable valve-operating system for an internal combustion engine according to an embodiment of the present invention;

FIG. 2 is an exploded perspective view of a principal part of the variable valve-operating system;

FIG. 3 is a perspective view showing a cam body of the variable valve-operating system in its entirety;

FIG. 4 is a side view of a boss as viewed from the direction indicated by arrow A in FIG. 3;

FIGS. 5 illustrates operating characteristics of the variable valve-operating system; and

FIG. 6 is a graph illustrating change in valve open period according to the operating characteristics.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will be described below with reference to FIGS. 1 through 6.

FIG. 1 is a sectional view of an internal combustion engine having a variable valve-operating system of the present invention incorporated, for example, in an intake valve system thereof. In FIG. 1, reference numeral 1 denotes a cylinder block (shown in FIG. 1 only) of, for example, a four-cylinder reciprocating gasoline engine (hereinafter merely referred to as engine), and 2 denotes a cylinder head attached to the head of the cylinder block 1.

First, the basic construction of the engine will be explained. The cylinder block 1 has four cylinders 4 (in FIG. 1, only two are shown) arranged in a row along the longitudinal direction of the engine. Each cylinder 4 has a piston 5 slidably received therein for reciprocating motion. The pistons 5 are coupled to a crankshaft of the engine by a connecting rod, though not shown.

The cylinder head 2 has combustion chambers 6 formed in its lower surface in a manner associated with the respective cylinders 4. Each of the combustion chambers 6 communicates with a pair of intake ports 7 and a pair of exhaust ports (not shown). Also, each combustion chamber 6 is provided with a pair of (two) intake valves 8 (valves) for opening and closing the respective intake ports 7 and a pair of exhaust valves (not shown) for opening and closing the respective exhaust ports. The intake valves 8 and the exhaust valves are each a normally closed type closed by a corresponding valve spring 9. Further, each combustion chamber 6 is equipped with a spark plug, not shown, such that a predetermined combustion cycle (four-stroke cycle including intake stroke, compression stroke, combustion and expansion stroke, and exhaust stroke) is repeatedly carried out.

An intake camshaft 10 (cam shaft) and an exhaust camshaft (not shown) extend through an upper portion of the cylinder head 2 along the row of the cylinders 4. The intake camshaft 10 and the exhaust camshaft are each connected to an end portion of the crankshaft (not shown) by a member such as a timing chain, not shown, so as to be rotated by the crankshaft.

As shown in FIG. 1, the intake camshaft 10 of the engine is fitted with a variable valve-operating system 15. The variable valve-operating system 15 employs a variable mechanism whereby constant-speed rotation of the camshaft is converted to non-constant-speed rotation to vary the valve open period of the intake valves 8. The variable mechanism is associated with each cylinder 4 and comprises a cam body 16 rotatably fitted around the outer peripheral surface of the intake camshaft 10 and an eccentric rotation-type valve open period-varying mechanism 28 combined with the corresponding cam body 16.

FIG. 2 is an exploded perspective view showing the cam body 16 and the valve open period-varying mechanism 28 associated with one cylinder.

Referring now to FIG. 2, the individual parts of the variable mechanism associated with each cylinder will be explained. The cam body 16 includes a cylindrical section 17 rotatably fitted around the outer peripheral surface of the intake camshaft 10, a pair of cam lobes 18 protruding radially outward from the outer peripheral surface of the cylindrical section 17, and a boss 19 protruding radially outward from an end of the cylindrical section 17 and located adjacent to one of the cam lobes 18. The cylindrical section 17 is rotatably supported, at its outer peripheral surface between the cam lobes 18, on the cylinder head 2 by a bearing 20 (shown in FIG. 1 only) arranged between the two intake valves 8.

As shown in the perspective view of FIG. 3 and the side view of FIG. 4, the boss 19 is generally triangular in shape and has a size slightly smaller than the nose 18 a of the cam lobe 18. Specifically, the boss 19 is a generally triangular block having a base 19 x protruding forward from the end of the cylindrical section 17 in the axial direction of the camshaft 10 and a center vertex 19 y projecting radially outward from the base circle of the cam lobe 18. The shape of the triangular boss 19 is nearly identical with (similar to) that of the nose 18 a of the cam lobe 18. The boss 19 is arranged such that when the cam body 16 is viewed in the axial direction of the camshaft 10, the boss 19 overlaps with the nose 18 a of the cam lobe 18, as shown in FIGS. 3 and 4. Specifically, the boss 19 is situated such that when the cam body 16 is viewed in the axial direction (the direction of arrow A) of the camshaft 10, the boss 19 is in its entirety located inside of the profile of the cam lobe 18. The boss 19 has a pin insertion hole 19 a cut in an outer end face thereof.

The cam face of each cam lobe 18 is disposed in direct contact with a follower of the corresponding intake valve 8, for example, a valve lifter 8 a attached to the proximal end of the intake valve 8, so that the intake valve 8 is driven by the cam lobe 18.

The valve open period-varying mechanism 28 comprises the combination of a non-constant speed mechanism 30 and a period setter 40 for setting the valve open period. The non-constant speed mechanism 30 converts constant-speed rotation of the intake camshaft 10 to non-constant-speed rotation to be transmitted to the cam body 16. Specifically, the non-constant speed mechanism 30 is constituted by an Oldham coupling.

As shown in FIGS. 1 and 2, the non-constant speed mechanism 30 includes an eccentric shaft 31 rotatably fitted around the outer peripheral surface of the intake camshaft 10 and located adjacent to the cam body 16, a harmonic ring 32 (intermediate rotating member) rotatably fitted around the outer peripheral surface of the eccentric shaft 31, and a driving arm member 33 fixed on a portion of the camshaft located between the harmonic ring 32 and the cam body 16. The outer periphery of the eccentric shaft 31 is eccentric with respect to the axis of the intake camshaft 10, and the harmonic ring 32 rotates around the outer peripheral surface of the eccentric shaft 31.

The driving arm member 33 includes a fixed ring 33 a fixed to the outer peripheral surface of the camshaft, and an arm 33 b projecting radially outward from a portion of the fixed ring 33 a shifted circumferentially by 180° from the boss 19. A pin insertion hole 34 is formed in the distal end of the arm 33 b and rotatably receives a connector pin 35 a. Another connector pin 35 b is rotatably supported by the pin insertion hole 19 a formed in the boss 19 of the cam body 16. An end portion of the connector pin 35 a projecting from the arm 33 b slidably engages with a radial slide groove 36a cut in the opposing end face of the harmonic ring 32. An end portion of the connector pin 35 b projecting from the boss 19 passes by the fixed ring 33 a and slidably engages with a radial slide groove 36 b formed in a position of the harmonic ring 32 shifted in the circumferential direction by 180° from the slide groove 36 a.

Consequently, rotation of the intake camshaft 10 is transmitted from the driving arm member 33 to the harmonic ring 32 through the connector pin 35 a, and then from the harmonic ring 32 to the cam body 16 through the connector pin 35 b and the boss 19. Specifically, rotation of the intake camshaft 10 is transmitted through the harmonic ring 32, which eccentrically rotates around the eccentric shaft 31 (around the intake camshaft 10) with a certain advance or retardation relative to the rotation of the camshaft 10 as shown in (a) and (c) of FIG. 5, to the cam body 16 while being converted to a rotation whose rotational phase relative to the rotational angle of the camshaft 10 periodically changes as indicated by the solid and dashed lines in (b) of FIG. 5.

The valve open period setter 40 comprises an input gear 41 formed integrally with the eccentric shaft 31 as a one-piece body. The input gear 41 is a round gear wheel coaxial with the intake camshaft 10, and when the input gear 41 is turned to set the valve open period, the axis of the eccentric shaft 31 eccentrically revolves around the axis of the intake camshaft 10. The individual parts of the valve open period setter 40 are configured taking account of the maximum lift of the intake valve 8, as shown in (a) to (c) of FIG. 5. When the axis β of the eccentric shaft 31 is located at an eccentric phase angle of 0° (upward offset) offset upward from the axis α of the intake camshaft 10 (remote from the valve) as shown in (c) of FIG. 5, the rotational phase of the cam lobe 18 relative to the rotational angle of the camshaft 10 is retarded to a maximum within the camshaft angular range from 0° to 180° and is advanced to a maximum within the angular range from 180° to 360°. Thus, when the valve open period setter 40 is set in the upward offset position, the valve open period is the shortest. On the other hand, when the axis β of the eccentric shaft 31 is located at an eccentric phase angle of 180° (downward offset) offset downward from the axis a of the intake camshaft 10 (toward the valve) as shown in (a) of FIG. 5, the rotational phase of the cam lobe 18 relative to the rotational angle of the camshaft 10 is advanced to a maximum within the camshaft angular range from 0° to 180° and is retarded to a maximum within the angular range from 180° to 360°. Thus, when the valve open period setter 40 is in the downward offset position, the valve open period is the longest. The valve open period can be varied by setting the eccentric phase angle to a desired angle between the two offset positions, namely, between 0° to 180°.

As shown in FIG. 1, each input gear 41 is meshed with a corresponding gear 42 a of a control shaft 42 (operating member). When an actuator (not shown) coupled with the control shaft 42 is controlled in accordance with the operating state of the engine, the angular position of the eccentricity of the harmonic ring 32 varies according to the engine operating state, so that the valve open period of the intake valves 8 associated with the respective cylinders 4 can be adjusted.

Operation of the variable valve-operating system 15 constructed as above will be now described.

Let it be assumed that the axis β of the eccentric shaft 31 is positioned by the actuator (not shown) at the eccentric phase angle 0° offset above the axis a of the intake camshaft 10, as shown in (c) of FIG. 5. Thus, the angular position of the eccentricity of the harmonic ring 32 is set in a predetermined position.

In this case, the cam lobe 18 disposed in contact with the intake valve 8 of each cylinder 4 is rotated such that the valve opening timing is retarded to a maximum while the valve closing timing is advanced to a maximum, as stated above. Consequently, the intake valve 8 opens and closes with such a characteristic as to provide the shortest valve open period suited for the low-speed operation of the engine, as indicated by the dashed line in FIG. 6.

On the other hand, where the axis β of the eccentric shaft 31 is turned 180° by the actuator to be set at the eccentric phase angle 180° offset below the axis α of the intake camshaft 10 as shown in (a) of FIG. 5, the angular position of the eccentricity of the harmonic ring 32 is set in another predetermined position.

In this case, the cam lobe 18 disposed in contact with the intake valve 8 of each cylinder 4 is rotated such that the valve opening timing is advanced to a maximum while the valve closing timing is retarded to a maximum, as stated above. As a consequence, the intake valve 8 opens and closes with such a characteristic as to provide the longest valve open period suited for the high-speed operation of the engine, as indicated by the solid line in FIG. 6. Needless to say, by changing the eccentric phase angle of the eccentric shaft 31 between 0° and 180°, it is possible to vary the valve open period of the intake valves 8 between the shortest and longest valve open periods indicated by the dashed and solid lines, respectively, in FIG. 6.

The boss 19 is arranged so as to be located in inside of the profile of the cam lobe 18, as viewed in the axial direction of the camshaft 10. Thus, when the cam lobe 18 pushes down the valve lifter 8 a (follower) of the intake valve 8 during the operation of the engine, the boss 19 remains located inside the profile of the cam lobe 18, as shown in FIG. 1, that is, no part of the boss 19 projects outward from the cam lobe 18. Also when the intake valve 8 returns to its closed position, the boss 19 remains situated inward of the profile of the cam lobe 18, as shown in FIG. 1, that is, no part of the boss 19 projects outside of the cam lobe 18. In this way, the boss 19 of the cam body 16 does not interfere with the valve lifter 8 a at all.

Accordingly, the cylindrical section 17 located between the boss 19 and the cam lobe 18 can be increased in thickness, making it possible to remarkably increase the mechanical strength of the base 19 x of the boss 19 and thus to heighten the maximum rotation speed of the engine. Specifically, the part (T) of the cylindrical section 17 located between the boss 19 and the cam lobe 18 can be increased in thickness up to the profile of the cam lobe 18, inclusive of the boss 19, as viewed from the axial direction of the camshaft 10.

Also, since the boss 19 is formed at a location corresponding to the nose 18 a of the cam lobe 18 as viewed in the axial direction of the camshaft 10, the largest possible area can be secured for increasing the thickness of the part T. Specifically, the thickness of the part T can be increased to the vicinity of the tip of the nose 18 a of the cam lobe 18, and therefore, the boss 19 as a whole, inclusive of the base 19 x, can be given sufficient rigidity and strength.

Moreover, the boss 19 of the cam body 16 can be positioned so as to overlap with the valve lifter 8 a of the intake valve 8 as viewed in the axial direction of the camshaft 10. Since the space limitation can be mitigated as a result, the individual parts of the variable valve-operating system 15 can be disposed more flexibly.

In the foregoing description of the embodiment, valve lifter is mentioned as the member driven by the cam, but such a member may alternatively be a rocker arm.

Also, in the above embodiment, the cam body 16 may be constructed such that the profile of the boss 19 as viewed in the axial direction of the camshaft 10 partly projects from the profile of the cam lobe 18. In this case, the boss 19 cannot be positioned so as to overlap with the valve lifter 8 a of the intake valve 8 as viewed in the axial direction of the camshaft 10. It is possible, however, to significantly increase the thickness of the part T of the cylindrical section 17 between the boss 19 and the cam lobe 18, so that the rigidity of the base of the boss 19 can be markedly enhanced by the increased thickness.

The present invention is not limited to the foregoing embodiment alone and may be modified in various ways without departing from the scope and spirits of the invention. For example, in the above description of the embodiment, the eccentric rotation-type variable valve-operating system of the present invention is applied to the intake system of the engine. Alternatively, the eccentric rotation-type variable valve-operating system of the invention may be applied to the exhaust system of the engine. 

1. A variable valve-operating system for an internal combustion engine, comprising: a cylinder head having an intake or exhaust valve; a camshaft rotatably supported by the cylinder head; a cam body rotatably fitted around an outer peripheral surface of the camshaft, the cam body including a cam lobe having an outer peripheral surface for driving the valve, and a boss protruding radially outward from an end portion of the cam body; and a valve open period-varying mechanism supported on the camshaft and including an intermediate rotating member having a center of rotation offset from an axis of the camshaft, the valve open period-varying mechanism being adapted to transmit rotation of the camshaft to the boss of the cam body through the intermediate rotating member and also permitting a valve open period of the valve to be varied through adjustment of an eccentric phase angle of the intermediate rotating member, wherein at least a part of the boss is so positioned as to overlap with a profile of a nose of the cam lobe when viewed in an axial direction of the cam body.
 2. The variable valve-operating system according to claim 1, wherein the boss is so positioned as to be located inside of the profile of the nose of the cam lobe when viewed in the axial direction of the cam body. 